Electrical resistance material.



UNITED STATES PATENT OFFICE. g

MATTHEW A. HUNTER, 0F TROY, NEW YORK.

ELECTRICAL RESISTANCE MATERIAL.

No Drawing.

To allwlwm it may concern:

Be it known that I, MATTHEW A. HUNTER, a. subject of the King of Great Britain, and a resident of Troy, county of Rensselaer, State of New York, have invented certain new and useful Improvements in Electrical Resistance Materials, of which the following is a specification.

My invention relates to electrical resistance material, and particularly to that class of electrical resistance material great durability is the predominant characteristic in connectionwith resistivity relatively higher than that of many metals, for example, silver, copper, etc. When 't is desired to derive heat directly from lectricity, the electricity is passed directly through a resistance material, the heat generated being proportioned to the resistance and the current. It is desirable that the resistance material be operated at as high a temperature as practicable, and the problem to be solved is to secure a material which has a relatively high resistance and which, at the same time, will not become oxidized or otherwise altered by the action of the air and moisture while it is at high temperature. In other words, durability is an essential characteristic. Another desirable characteristic is that the temperature coefficient of resistance must be low. The best known resistance material, so far as durability is concerned, is the element platinum. The high cost of this element renders its general use as resistance material prohibitive. \Vhile platinum has a higher resistance than some elements, its resistance is not great as compared With some alloys of less durability. The resistance materials comprising these alloys that are well known have sufficient durability to render them practicable and a higher resistance than that of platinum, ,but they can only be prepared at great cost, because of the great value of their basic constituents, and because of the difiiculty'experienced in reducing the material to shapes and sizes necessary for their general application in the heating devices.

The alloy which I have discovered and which embodies my invention is superior to the expensive alloys above mentioned, so far as durability, resistivity and temperature coeflicient of resistance are concerned, but it, nevertheless, is cheaply produced, by reason of the low cost of its basic and fundamental constituent, iron, and byv reason of its ready Specification of Letters Patent.

wherein Application filed August 9, 1916. Serial No. 113,880.

workability. It has been the belief, heretofore, that iron was not a suitable base or foundation for a practical resistance material, because of its being readily destroyed by exposure to air at high temperature, even when alloyed with elements known to possess the property of resisting oxidation at hlgh temperatures. It is well known, however, that the properties of an alloy cannot be foretold from a knowledge of the properties of the constituents of the alloy derived from observation of the properties of those constituents under variations of conditlons, either when they are substantially purelor when they are alloyed with other maeria s..

My invention comprises an alloy wherein the base or foundation is iron, which, as above noted, has heretofore been believed to be unsuitable, with which is alloyed nickel and chromium, the proportions of nickel and chromium being respectively less than the proportion of iron. It has been suggested that chromium will increase the resistance of an alloy and, at the same time, increase its durability, but it is well known that the addition of chromium in all percentages will not bring about these desirable results, but, on the contrary, the addition of chromium in certain percentages will exert an undesirable influence upon resistivity and durability.

I have made a great number of experiments with alloys containing chromium,

iron and nickel. My experiments havehad for their object the determination of the resistivity and durability of alloys in which various amounts of chromium have been added to alloys having varying. proportions of iron and nickel. The alloys which were tested comprised a number of series, in each of WhlCh the chromium content remalned constant and the proportions of iron andparts nickel and 0 parts iron. Each series of alloys above referred to was formed by adding a constant uantity of chromium to a Varying ironnic rel alloy, the constant quantity of chromium in one series differing from that in another and varying substantially from 10 to 40 parts for each 10Q parts of the iron-nickel portion. In. each series I found that the best results are obtained with an alloy in which the iron-nickel portion has from 75 parts nickel and 25 parts iron to 25 parts nickel and 75 parts iron and the chromium portion comprises 20 to %10 arts of chromium for each 100 parts of the ironnickel portion. Very desirable alloys are found in the field in which the iron-nickel portion is made up of 50 to 60 parts of iron and 50 to 40 parts of nickel and the chromium portion varies from 25 to 35 parts of chromium for each 100 parts of the ironnickel portion. As a specific instance, I have found that an alloy containing 30%. nickel, 47% iron and 23% chromium gives excellent resuits: "This alloy has as high resistivity as is desirable and has great durability, and it is, at the same time, very easily worked and much cheaper than known alloys having equally desirable properties. This alloy is readily compounded, and great uniformity of results is obtained.

It is to be understood that, where I have mentioned chromium, other elements of the group to which chromium belongs can be substituted 'within the scope of my invention. Iron, nickel and cobalt are in the same group of elements, but it has been believed heretofore that iron could not be substituted for nickel. In my alloy, however, I have successfully made this substitutio by using the proportions herein set forth of the various elements. It is to be understood, however, that cobalt may be substituted for nlckel within the scope of my invention, and it is to be understood that whenever I refer to a metal having'the properties of nickel and cobalt, in the claims, I intend only the metalsnickel and cobalt, inasmuch as'they have common properties, suitable for my purposes, but which can not be defined by any single term. The metalsof the chromium group, when alloyed in proper proportions with other metals, impart desirable properties thereto. However, at present I believe that chromium is the most desirable of the metals of this group. It has thus been found to be satisfactory for my purposes.

It is apparent, therefore, that I have produced an alloy having an element for a base Which was believed formerly to be unsuitable, and which alloy, nevertheless, possesses the necessary characteristics to a marked degree.

It will be understood, of course, that while I have described my invention in its. referred form, I do not intend it to be limlted to the specific proportions set forth, except as set forth in the claims, and it is understood that various other metals may be added to secure the advantages of the properties imparted by the addition thereof.

Having thus described my invention, what I claim and desire to secure by Letters Patent is 1. An electric resistance material comprising a strip, strand or filament formed of an alloy of iron, a metal of the chromium group, and a metal having the properties of nickel and cobalt, no other metal being present in such proportions as to afi'ect the qualities of said alloy as a resistance material.

2. An electric resistance material comprising a strip, strand or filament formed of an alloy having a major portion of iron, a metal of the chromium group, and a metal having the properties of nickel and cobalt.

3. An electric resistance material comprising an iron-nickel ortion comprising one hundred parts wherein iron is present in the proportion of more than fifty parts and a metal having the properties of nickel and cobalt is present in the proportion of less than fifty parts, and a chromium portion in which a metal of the chromium group is present in the proportion of more than twenty arts of such last named metal to one hundred parts of nickel and iron.

4. An electric resistance material comprising an iron-nickel portion comprising one hundred parts wherein iron is present in the proportion of seventy five to twenty five parts and a metal having the properties of nickel and cobalt is present in the proportion of twenty five to seventy five parts, and

a chromium portion in which a metal of the chromium group is present in the proportion of ten' 'to thirty parts of such last named metal to one hundred parts of nickel andlI'OIl.

5. An electric resistance material com prising iron, a metal having the properties of nickel and cobalt and a metal of the chromium group, the proportion of iron being substantially equal to the other elements together. i

6. An electric resistance material com- 'together and the proportions of the other elements being substantially equal.

In testimony whereof, I have signed my name to this specification.

1- MATTHEW HUNTER. 

